The present application generally relates to a hybrid inflator which is used to inflate an air bag.
Inflatable bag restraint systems have been shown to reduce the seriousness of injuries and number of fatalities resulting in motor vehicle accidents. There exists a number of means for inflating an air cushion or air bag such as utilizing a quantity of stored gas which is selectively released to expand the air bag. Alternatively, a gas source derived from a gas generating material propellant such as sodium azide, which upon ignition thereof generates a sufficient quantity of gas to expand the air bag. Another type of gas source results from a combination of the stored compressed gas and a gas generating or enhancing material. This last device is often referred to as an augmented gas or hybrid inflator. Various hybrid inflators have been shown in the past such as those illustrated in U.S. Pat. Nos. 3,756,621 and 3,895,821. The inflator shown in U.S. Pat. No. 3,756,621 uses a separate squib or initiator to ignite the propellant and an actuator to open an exit passage to initiate compressed gas flow. U.S. Pat. No. 3,895,821 mounted a single squib outside the pressurized environment of the pressure vessel to ignite the propellant.
U.S. Pat. Nos. 3,891,233 and 3,901,530 illustrate what is called a driver side air bag inflator. With reference to U.S. Pat. No. 3,901,530 there is illustrated a hybrid inflator which utilizes an initiator and a quantity of propellant. This inflator includes a plurality of burst disks which are opened initially by the high temperature produced by the burning initiator and propellant. One disadvantage of this prior art inflator is that the products of combustion are transferred directly into the air bag. Another disadvantage is that during the initial inflation of the air bag very hot gases are produced. As is often the case, the burn time of a propellent is less than the total discharge time of the stored gas and as such, the initial hot inflation gases are followed by the remaining cooler gas stored in the inflator. In contrast, the present invention will improve the heat transfer process between the initiator, propellant and stored gas to yield a more uniformly heated quantity of inflation gas. Further, as will be seen from the description below, the present invention will cause an outlet burst disk to open primarily due to the overpressurization of the stored inflation gas. This overpressurization is achieved by heating the stored gas by products of combustion of the burning propellant. In this manner, the inflation gases initially communicated to the air bag are cooler than those developed in the prior art, thereby minimizing damage to the air bag, the air bag cover, and related mounting hardware. These deficiencies are avoided in the present invention.
It is an object of the present invention to provide an improved hybrid inflator. A further object of the present invention is to provide a hybrid inflator in which certain products of combustion become plated on the internal walls of a pressure vessel thereby lessening particulate emission.
Accordingly, the invention comprises: a device for inflating an air bag comprising: a pressure vessel formed by a vessel part and a generator body assembly. The generator body assembly is received within opposing openings in the vessel part (22) and secured thereto to provide a gas tight seal. The generator body assembly includes: a first bore to receive a quantity of propellant and initiator assembly means to cause the propellant to burn in response to a control signal indicative of a vehicle crash. The generator body assembly further includes at least one radial passage directed toward an internal wall of the pressure vessel such that some of the products of combustion of the burning propellant will impinge thereon and plate thereto. A first burst disk is provided to seal the at least one radial passage and pressure vessel. The first burst disk is opened by the products of combustion permitting same to flow into the pressure vessel and heat the gas stored therein. The gas generator assembly also includes a plurality of flow passages communicating with the pressure vessel to an outlet passage, and a outlet burst disk disposed relative to exit ends of the flow passages and to an outlet passage to provide a gas tight seal. The outlet seal is ruptured as a result of increased gas pressure in the pressure vessel (34) resulting from heating due to the burning of the propellant.
Many other objects and purposes of the invention will be clear from the following detailed description of the drawings.